The invention relates to a method for cleaning a nozzle outlet surface on a print head of an ink jet printer, more specifically, by a cleaning head, the ink being wiped off the nozzle outlet surface by a doctor blade on the cleaning head and being sucked away by a vacuum generator connected to the cleaning head, and also relates to a device for cleaning a nozzle outlet surface on a print head of an ink jet printer by a cleaning head which, more specifically, includes a doctor blade, the cleaning head further having a vacuum generator connected thereto.
A problem which often occurs in ink jet printers is that ink residues and paper dust collect on the nozzle outlet surfaces, so that they have to be wiped off frequently.
For this purpose, a wiping device described in the published German Patent Document DE 40 00 454 C2 can be used. The wiping device described in this published document has only a single doctor blade, referred to therein as an upper lip.
It is possible that the doctor blade, as it sweeps over the nozzle outlet surface, does not pick up all the contaminants and residues which are to be removed. Consequently, the nozzle outlet surface must be wiped off many times with the doctor blade, so that the expenditure of time for the cleaning, and the time during which the ink jet printer is at a standstill, are markedly increased.
A further shortcoming of the wiping device described in the foregoing German document is apparent from the fact that a vacuum pump thereof sucks in a considerable flow of outside air through the suction hole thereof which is open to the surroundings, this flow of outside air not only causing a low efficiency of the device, but also opposing the sucking of the ink out of the interior of the nozzle.
The wiping device has a cleaning head that includes a carrier part connected to the vacuum pump and having the wiping lip inserted therein. In order to clean the nozzle outlet surface, the cleaning head is disposed above the latter. In the case of such an arrangement, no assurance is provided that, after the nozzle outlet surface has been cleaned, no ink will drip back from the cleaning head onto the nozzle outlet surface.
A print head, which is referred to as a printer carriage in the published German document and can be wiped off by the wiping device, is moved relative to the stationary wiping lip, so that the latter brushes or streaks over the nozzle outlet surface on the print head. Although such a construction may indeed be suitable for a lightweight printer carriage having a relatively small-area nozzle outlet surface with only a few nozzles, it is not suitable for a heavier print head. In order to print large printing-material formats at high printing speeds, a print head having a large-area nozzle outlet surface equipped with a relatively large number of nozzles is more suitable. However, such a print head is generally also comparatively heavy and, because of the mass moment of inertia thereof, requires a complex drive mechanism, a high drive power and a large free movement space, in order to be able to move the print head relative to the wiping lip.
The state of the prior art may be further ascertained from the published German Patent Document DE 197 04 003 A1, the published European Patent Document EP 0 389 481 B1 and U.S. Pat. No. 5,730,538.
It is accordingly an object of the invention to provide a method and a device for cleaning a nozzle outlet surface on a print head of an ink jet printer by which the nozzle outlet surface can be cleaned quickly and thoroughly.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method for cleaning a nozzle outlet surface on a print head of an ink jet printer by a cleaning head, the ink being wiped off the nozzle outlet surface by a doctor blade on the cleaning head and being sucked away by a vacuum generator connected to the cleaning head, which comprises sucking the ink out of the interior of at least one nozzle on the nozzle outlet surface, by forming with the cleaning head an evacuation chamber over the opening, applying vacuum to the evacuation chamber by the vacuum generator, and hermetically sealing off the evacuation chamber.
In accordance with another mode, the method of the invention includes effecting the sealing off of the evacuation chamber by the doctor blade by the engagement thereof with the nozzle outlet surface.
In accordance with a further mode, the method of the invention includes hermetically sealing off the evacuation chamber by an additional doctor blade on the cleaning head by the engagement of the additional doctor blade likewise with the nozzle outlet surface.
In accordance with another aspect of the invention, there is provided a device for cleaning a nozzle outlet surface on a print head of an ink jet printer by a cleaning head formed of a doctor blade and connected to a vacuum generator, the cleaning head comprising at least one additional doctor blade.
In accordance with another feature of the invention, the device includes an evacuation chamber formed between the doctor blades in the cleaning head and being subjectible to suction air and vacuum, respectively, applicable by the vacuum generator.
In accordance with a further feature of the invention, the doctor blades are arranged as seals for sealing off the evacuation chamber between the cleaning head and the nozzle outlet surface.
In accordance with an added feature of the invention, the device includes a motor for moving the cleaning head parallel to the nozzle outlet surface via a first mechanism and/or toward and away from the nozzle outlet surface via a second mechanism.
In accordance with an additional feature of the invention, the first mechanism is a flexible drive mechanism.
In accordance with yet another feature of the invention, the mechanism is a cam control.
In accordance with yet a further feature of the invention, the cleaning head is disposed underneath the nozzle outlet surface.
In accordance with yet an added feature of the invention, the cleaning head is connected to the print head via an ink circuit.
In accordance with yet an additional feature of the invention, the cleaning head has at least three doctor blades.
In accordance with a further aspect of the invention, there is provided an ink jet printer having a device for cleaning a nozzle outlet surface on a print head of the ink jet printer by a cleaning head formed of a doctor blade and connected to a vacuum generator, the cleaning head comprising at least one additional doctor blade.
In accordance with another feature of the invention, the ink jet printer comprises a printing module and a cleaning module, the modules being of compatible construction so that the cleaning module is combinable with the printing module when appropriate.
In accordance with an additional aspect of the invention, there is provided an offset and/or rotary printing machine integrated with the ink jet printer having at least one of the foregoing features.
In accordance with a concomitant aspect of the invention, there is provided an offset and/or rotary printing machine coupled for in-line operation with an ink jet printer having at least one of the foregoing features.
The term xe2x80x9cinkxe2x80x9d used in connection with the invention comprises both water-based inks and inks of a different composition, for example radiation-curing inks, so-called ultraviolet or UV inks, which can be printed by the ink jet printer.
The ink in the print head sometimes tends to form air bubbles, which collect in the corners within the print head and the nozzles.
An advantage offered by the method according to the invention is that these air inclusions can be removed from the nozzle orifices together with the ink, so that printing faults caused by the air inclusions are avoided. Also, as the nozzle outlet surface is squeegeed or doctored off, paper dust wiped into the nozzle orifice can be sucked reliably out of the nozzle orifice, via the evacuation chamber and the nozzle opening, due to the application of vacuum to the nozzle orifice.
Because the evacuation chamber formed by the cleaning head together with the nozzle outlet surface is sealed off hermetically, the action of sucking outside air into the latter is ruled out or at least restricted to such an extent that it does not impair the function thereof. In order to seal off the gap between the cleaning head and the nozzle outlet surface hermetically, the cleaning head can have a single or multi-partite seal. The seal pressed by the cleaning head onto the nozzle outlet surface can slide along on the latter and, consequently from time to time, surround the opening or openings in the nozzle or nozzles, respectively, to which suction is to be applied, as a result of which the vacuum in the evacuation chamber, which is open toward the nozzle outlet surface or, in other words, is closed by the nozzle outlet surface, also becomes effective in the nozzle orifice or the nozzle orifices, respectively. The seal is preferably composed of an abrasion-resistant and resilient material, for example of rubber, polyurethane or other polymer. The seal is preferably formed by the doctor blade or a number of doctor blades on the cleaning head. For this purpose, the doctor blade or doctor blades can be composed of one of the aforementioned materials and constructed as resilient wiping lips.
An advantage provided by the device according to the invention is that as the nozzle outlet surface is wiped off, soil or contaminants which are not picked up by the first doctor blade initially sweeping over the nozzle outlet surface are picked up by the second doctor blade, which sweeps over the nozzle outlet surface immediately following the first doctor blade.
The doctor blades can be formed on the cleaning head, both the cleaning head and the doctor blades being constructed as a single component, for example as a single injection-molded part made of polyurethane.
The doctor blades are preferably fitted to the cleaning head and are composed of a different material from that of the cleaning head. This is advantageous from the point of view of a dimensionally stable construction of the cleaning head, which is composed of a hard polymer, for example, and a soft, resilient construction of the doctor blades, which are composed of rubber, for example. The doctor blades can be affixed to the cleaning head so that they can easily be replaced and, for example, can be clamped into the cleaning head. If abrasive wear of the doctor blades should occur, the worn doctor blades can thus easily be detached from the cleaning head, without replacing the complete cleaning head, and replaced by new doctor blades.
In an embodiment of the device which is advantageous with regard to applying vacuum to the nozzle to be cleaned, the vacuum generator terminates or opens between the doctor blades in the cleaning head, the opening forming an evacuation chamber to which vacuum can be applied in the interspace between the doctor blades, which from time to time is aligned with the opening of the nozzle to be cleaned, due to the wiping movement. It is preferable for a suction line, which connects the vacuum generator to the cleaning head, to terminate or open between the two doctor blades.
In an embodiment which is advantageous with regard to cost-effective production, the doctor blades are formed multifunctionally as seals, and seal off the evacuation chamber between the cleaning head and the nozzle outlet surface.
In an embodiment which is advantageous with regard to cleaning a large and heavy print head having a nozzle outlet surface that is provided with many rows of nozzles, the cleaning head can be moved along the nozzle outlet surface via a first mechanism and/or towards and away from the nozzle outlet surface again via a second mechanism. Due to the fact that, in this case, the cleaning head is movable by a motor, it is possible for the print head to remain in position during the cleaning operation. A single electric motor is preferably used both for driving the cleaning head horizontally along the nozzle outlet surface via the first mechanism and also for driving the cleaning head vertically relative to the nozzle outlet surface via the second mechanism.
In an embodiment which is advantageous with regard to driving the cleaning head horizontally and vertically by the same motor, the first mechanism is a mechanism from the group of flexible drive mechanisms. In such a flexible drive mechanism, two non-adjacent elements of the mechanism are coupled via a supple flexible drive member (belt, tape, cord) or multi-link flexible drive member (chain). The transmission of movement from one element in the mechanism to the other element in the mechanism via the flexible drive is performed by friction, by pairing shapes or by fastening the flexible drive member to the elements of the mechanism, which may be pulleys for example. The flexible drive member may be a closed member, i.e., endless, or open. The flexible drive member can be driven so as to revolve continuously in one direction of revolution or preferably reciprocatingly, i.e., alternately in two different directions of motion. It is preferable if two gear wheels form the coupled elements in the mechanism, and a toothed belt meshing with the gear wheels forms the flexible drive member.
In an embodiment which is likewise advantageous with regard to driving the cleaning head both horizontally and vertically by the same motor, the second mechanism is a cam mechanism. It is preferable for the cam or cam control of the planar cam mechanism to be arranged immovably on the device, and the cleaning head to be guided along the cam, in contact with the latter, by the first mechanism. In addition, the cam can be contoured in such a way that it moves or lifts the cleaning head towards the nozzle outlet surface and moves or lowers it away from the nozzle outlet surface. The cam contour thus has the effect of bringing the doctor blades to bear on the nozzle outlet surface from a position located at a distance therefrom, of holding the doctor blades in contact with the nozzle outlet surface from time to time as the doctor blades sweep across the latter, and of again positioning the doctor blades at a distance from the nozzle outlet surface. The cam can be an appropriately contoured guide rail or guide groove, which forces upon the cleaning head a movement component that is at right angles to the nozzle outlet surface. The cleaning head can be constructed as a slide which slides along the cam contour. The cleaning head is preferably formed as a carriage which rolls along the cam contour.
In an embodiment that is advantageous with regard to avoiding ink dripping out of the cleaning head again or seeping onto the nozzle outlet surface, the cleaning head and the doctor blades are arranged underneath the nozzle outlet surface, so that they can move along the latter. This arrangement of the cleaning head is also advantageous with regard to carrying away the ink squeegeed or doctored off the nozzle outlet surface and often heavily soiled or contaminated with paper dust. This ink does not have to be sucked away by the vacuum generator but can flow over the back of one or more of the doctor blades into that part of the cleaning head located under the doctor blades and from this part into a collecting container, under the action of gravity.
In an embodiment which is advantageous with regard to re-using the ink sucked out of the interior of the nozzles for printing, the cleaning head is connected to the print head via a return line system. The return line system can be an ink circuit which is open to the surroundings or is closed. Parts of the return line system are the vacuum generator and the suction line opening in the cleaning head. Although the ink sucked out of the nozzle orifices contains air inclusions which interfere with printing and which disintegrate after the ink has been sucked away, the ink which has been sucked away, by contrast with the ink squeegeed or doctored off the nozzle outlet surface, is barely soiled or contaminated by paper dust or other ink that has been wiped off. It is therefore very expedient, from an ecological and economical point of view, not to dispose of the ink which has been sucked away in the same way as the ink which has been squeegeed or doctored off, but to use it for printing. The advantageous separation of the ink which has been squeegeed or doctored off, from the ink which has been sucked away, is made possible simply by preceding each of the doctor blades, as viewed in the wiping direction, by an outlet or extraction duct leading into the cleaning head. The first doctor blade, as viewed in the direction of movement of the doctor blades, can be preceded by an outlet duct for the ink squeegeed or doctored off, and the second doctor blade can be preceded by the suction line opening between that doctor blade and the first doctor blade as an extraction duct for the re-usable ink.
In an embodiment which is advantageous with regard to the integration of the ink jet printer into an offset and/or rotary printing machine, or coupled in-line operation of the ink jet printer with the printing machine, the ink jet printer is of modular construction and comprises a printing module with the print head, and a cleaning module to which the cleaning head and the mechanisms moving the latter belong. In order to clean the print head, the cleaning module can be assembled with the printing module of the ink jet printer and removed from the printing module again following the cleaning.
For example, the cleaning module can be inserted as required into the ink jet printer and/or the printing machine and, after the cleaning, can be withdrawn again. The ink jet printer and/or the printing machine can have a window formed in the side wall thereof through which the cleaning module can be pushed. It is preferable for the horizontal insertion direction of the cleaning module to be at right angles to the printing-material transport direction of the printing machine and/or to that of the ink jet printer and also at right angles to the direction of motion of the cleaning head along the nozzle outlet surface.
The easily transportable cleaning module of the assemblable ink jet printer, which is of modular construction, is is preferably constructed so as to correspond with the device according to the invention and can also be a cleaning device having a construction differing therefrom, yet being appropriately compatible so that it is assemblable with the remaining ink jet printer for the purpose of cleaning the print head.
The ink jet printer is preferably assigned to an offset printing machine, which can be a rotary printing machine, or to a rotary printing machine, which can be an offset printing machine, for combined operation as the impression or numbering unit thereof. Using the printing machine, sheet printing material already printed in many colors can thus advantageously be printed by the ink jet printer with individualized codes, for example changing bar codes, consecutive numbers or different recipient addresses, as well. For this purpose, the ink jet printer can be integrated into the printing machine, following the last offset printing device in the printing machine as viewed in the printing-material transport direction. For this purpose, however, the ink jet printer can also be coupled to the printing machine via a printing-material transport device which transports the printing material from the printing machine to the ink jet printer. The transport device can be a conveyor belt, for example, whereon printing-material sheets printed in the printing machine are transported to the ink jet printer. The conveyor belt can extend into the ink jet printer, so that the printing-material sheet resting on the conveyor belt can be printed by the print head in the ink jet process.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for cleaning a nozzle outlet surface on a print head of an ink jet printer, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings, wherein: